The present invention relates to the development of a hip joint prosthesis of the kind disclosed in WO 89/11837. This document inter alia discloses a hip joint prosthesis comprising a primary fixture in the shape of a sleeve which is intended to be inserted into a central hole bored longitudinally through the collum femoris from the outer side of the femur and a secondary fixture in the shape of a cap having a spherical shape intended to be attached to and cover the end of the collum femoris when the head of the collum has been partially or entirely removed and the outside of the remaining end has been cut to a cylindrical shape. The primary and secondary fixtures are interconnected by means of a bolt which at one end has an internal thread. The bolt is to be inserted into the sleeve and its internal thread is to be made to engage a central, threaded stud projecting from the spherical cap. When the bolt is tightened, the cap is pressed over the cylindrically cut caput or end of the collum.
The prior art device thus is relatively complicated, both in terms of its construction and use.
In some applications, however, it may not be suitable to use this type of prior art device. One reason for this is that the shape of the collum may make it difficult to retain enough cortical bone to give the secondary fixture of cap a firm support, since the shape of the collum may vary to a great extent.
This prior device is also designed to be inserted in a two-step procedure; i.e., some parts of the prosthesis are to be inserted in a first operation, and the remaining parts are subsequently in a second operation after a healing period of a few months.
Other similar prior art is disclosed for instance in DE-A1-28 45 231, DE-A1-27 24 040, United U.S. Pat. No. 4,795,473 and U.S. Pat. No. 4,005,495.
The object of the present invention is to provide a hip joint prosthesis which is simple in construction and use and which is particularly suited for insertion in a one-step operation, and which can also be adapted to fit different conditions.